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--- nsw_lidar [2018/10/06 14:48] – [Contours] allchin09
+++ nsw_lidar [2024/04/05 19:00] (current) – Add download bushwalking
@@ Line 1: / Line 1: @@
-Page for documenting NSW lidar processing
+====== Mapping from NSW Lidar with QGIS ======
-====== Intro ======
 NSW Spatial Services have undertaken a program to map all of NSW using lidar (light detecting and ranging)
 For details, see information on their [[http://spatialservices.finance.nsw.gov.au/mapping_and_imagery/environmental_spatial_programs|elevation program]].
-Elevation data can best be accessed through the [[http://elevation.fsdf.org.au/|Geoscience Australia ELVIS program]], and then processed with a GIS such as [[https://www.qgis.org/en/site/index.html|QGIS]] to create useful topographic maps.
+Elevation data can best be accessed through the [[http://elevation.fsdf.org.au/|Geoscience Australia ELVIS program]].
-====== Resources ======
+It can then processed with a GIS such as [[https://www.qgis.org/en/site/index.html|QGIS]] to create useful topographic maps. Instructions below are specifically for use with QGIS, though the general outline may be useful for other GISs.
-  * [[https://www.tandfonline.com/doi/full/10.1080/23729333.2017.1300998|A design of contour generation for topographic maps with adaptive DEM smoothing]]
-  * [[http://www.jennessent.com/downloads/tpi-poster-tnc_18x22.pdf|Poster on TPI]]
-====== Topographic maps ======
+====== Topics ======
-There are several primary data items for topographic maps that can be generated using the DEM data from the NSW Lidar. The main ones are:
+The original topics here have now been moved to their own pages.
-  * Contours
-  * Hydrology (Stream Network)
-  * Clifflines
-The steps below are works in progress to determine effective (the best?) ways to extract the various items out of the DEM data for use in topographic maps. Any feedback/suggestions of improvements are welcome.
+Any feedback/suggestions of improvements are welcome.
-===== Contours =====
+===== Managing DEMs =====
-See page on [[[qgis_contour_labelling|QGIS Contour Labelling]]
-===== Hydrology (Stream Network) =====
-===== Clifflines =====
+  * [[nsw_download_dems|Downloading DEMs]] - how to download DEMs from the ELVIS service
+  * [[nsw_merge_dems|Merging DEMs]] - how to merge DEMs in QGIS
+  * [[nsw_dems|Managing large DEMs]] - while data can be downloaded in an ad hoc manner, if you are regularly processing NSW DEMs, it is better to have the DEM tiles already downloaded. This page provides steps to do this in an automated manner.
-The steps below have been tested in the Blue Mountains, a region that has a significant number of relatively vertical sandstone cliffs. It may be less effective in different terrain.
+===== Topographic maps =====
-==== Initial analysis of slope, aspect ====
+There are several primary data items for topographic maps that can be generated using the DEM data from the NSW Lidar.
-SAGA -> Terrain Analysis - Morphometry -> Slope, Aspect, Curvature
+  * [[qgis_depressionless_dem|Hydrologically correct DEM]] - prior to further operations, it is usually important to make sure that your DEM is free of depressions. Otherwise these will mess up streams and possibly contours.
-Extract
+Once you have a depressionless DEM, the following items can be generated:
-	Slope, Aspect
+  * [[qgis_contours|Contours]]
-using DEM and [1] Maximum Triangle Slope (Tarboton (1997)). I haven't tested any other algorithms.
+  * [[qgis_hydrology|Hydrology (Stream Network)]]
+  * [[qgis_slope|Slopes]] - while not a standard feature of topographic maps, this can be a simple way to identify cliffs
-Cliff areas can be identified using a range of 60-90 and 70-90 degrees on the Slope file. Using 60-90 degrees helps connect logical cliffs and avoid small breaks.
+  * [[qgis_clifflines|Clifflines]] - a work in progress
-==== Initial Cleaning ====
+===== Styles =====
-Next convert data to 1 bit (1,2 not 0,1, as Sieve ignores 0s) using Raster Calculator.
+  * [[qgis_styling|Styling]] - download basic style files
-Formula is: (Slope > 0) + 1
-Then Sieve resulting data using a Threshold of 100 and 8-connectedness to get rid of small non-connected cliffs. Note above that Sieve doesn't like 0s.
+===== Automation =====
-Also good to rerun Sieve with smaller Threshold (1-10) and 4-connectedness to
-a) get rid of some small dangles.
-b) fill small holes.
-Additional smoothing can be done using a User Defined Filter with the following matrix. This will apply some smoothing by allowing you to reclassify the pixel values, and remove single pixel indentations like this:
-    000
--> 111
-    111
-and single pixel protrusions like this:
-    000
--> 000
-    111
-The main problem is that the matrix has to be defined each time in QGIS. There doesn't seem to be an option to load it. Possibly this can be done outside QGIS.
+  * [[qgis_basic_automation|Basic map creation]] - a set of PyQGIS scripts that will create (and optionally save) a basic topographic map. This map can be used in QField
-Matrix is:
+===== Mobile apps =====
-.0 0.5 0.0
-.5 0.5 0.5
-.0 0.5 0.0
-If the original matrix is 0/1 then the cutoff will be 1.5
+  * [[qgis_qfield|QField]] - QField is an excellent Android app for for viewing projects created with QGIS
+  * [[https://merginmaps.com/|Mergin Maps]] - (Previously Input App) is a mobile app compatible with QGIS
-If the original matrix is 1/2 then the cutoff will be 3.5
+===== Dumping Ground / WIP =====
-This step could be run multiple times - some testing would need to be done to determine how many times.
+==== Resources ====
+  * [[https://www.tandfonline.com/doi/full/10.1080/23729333.2017.1300998|A design of contour generation for topographic maps with adaptive DEM smoothing]]
-Other options for cleaning the data include a plugin called LecoS, but this doesn't work on QGIS 3. Another possibility is Shrink and Expand - radius 1? But this also creates some new holes that didn't previously exist, so not ideal.
+  * [[http://www.jennessent.com/downloads/tpi-poster-tnc_18x22.pdf|Poster on TPI by Andrew D. Weiss]]
-==== Thinning ====
+[[https://grass.osgeo.org/grass78/manuals/addons/r.geomorphon.html|GRASS - r.geomorphon function information page]]. This is a different approach that could be taken for landform classification. Yet to be tested.
-Convert back to 0/1 data using Raster Calculator
+[[https://docs.qgis.org/3.4/en/docs/training_manual/grass/grass_setup.html|Training lession for QGIS 3.4 on GRASS Setup and basic use]]. Specific GRASS setup is required to use any GRASS functions in QGIS.
-Use Translate: set Output Data Type = Byte, set NoData = 0
+[[https://grasswiki.osgeo.org/wiki/Introduction_to_GRASS_GIS_with_terrain_analysis_examples|GRASS GIS example of terrain analysis using r.geomorphon]]
-Run r.thin - r.thin is quite picky about the input file format. Needs to be NULL/non-NULL (not float or int). The Translate process above provides this. The previous two steps could be combined into one. Also, this file may need to be explicitly saved (not just a temporary file?!)
+[[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.706.8909&rep=rep1&type=pdf|Geomorphons - a pattern recognition approach to classification and mapping of landforms]] paper.
-==== Vectorising ====
+[[https://whiteboxgeospatial.wordpress.com/2014/12/25/a-new-form-of-multi-scale-topographic-position-visualization/|Multiscale topographic position - WhiteboxTools]] blog post.
-Run r.to.vect: set Feature Type = line
+[[https://jblindsay.github.io/wbt_book/available_tools/geomorphometric_analysis.html#multiscaletopographicpositionimage|Multiscale topographic position image - WhiteboxTools function - user manual entry]]
+==== Method ====
+The below snip of Breakfast Creek makes use of TPI calculated from a LIDAR derived DEM. Only positive values for TPI as displayed, which indicate cliff-like features. It is then combined with contours and aerial imagery to convey the terrain of the area.
-Run v.clean: Cleaning Tool = rmdangle, Threshold = 5,10
+{{:breakfast_creek_snip.jpg?400|TPI from LIDAR DEM combined with contours and imagery to show clifflines and terrain}}